Vibration-attenuating hard-mounted pylon

ABSTRACT

A preferred embodiment of a pylon has six pylon mounting links for mounting the pylon to an airframe. Each link is considered “near-rigid” and has a spherical-bearing rod-end on both ends such that the link can only transmit axial loads. At least one of the links has a mass carried within the link and selectively moveable by an actuating means along the axis of the link in an oscillatory manner for attenuating vibrations traveling axially through the link. The actuating means may be an electromechanical, hydraulic, pneumatic, or piezoelectric system. By mounting each link in a selected orientation relative to the other links, the actuating means may be operated in a manner that attenuates axial vibration that would otherwise be transmitted through the link and into the airframe.

TECHNICAL FIELD

The present invention relates generally to the field of active vibrationcontrol and relates particularly to active vibration control foraircraft.

DESCRIPTION OF THE PRIOR ART

For many years, effort has been directed toward the design of apparatusfor isolating a vibrating body from transmitting its vibrations toanother body. Such apparatus are useful in a variety of technical fieldsin which it is desirable to isolate the vibration of an oscillating orvibrating device, such as an engine, from the remainder of thestructure. Typical vibration isolation and attenuation devices(“isolators”) employ various combinations of the mechanical systemelements (springs and mass) to adjust the frequency responsecharacteristics of the overall system to achieve acceptable levels ofvibration in the structures of interest in the system. One field inwhich these isolators find a great deal of use is in aircraft, whereinvibration-isolation systems are utilized to isolate the fuselage orother portions of an aircraft from mechanical vibrations, such asharmonic vibrations, which are associated with the propulsion system,and which arise from the engine, transmission, and propellers or rotorsof the aircraft.

Vibration isolators are distinguishable from damping devices in theprior art that are erroneously referred to as “isolators.” A simpleforce equation for vibration is set forth as follows:F=m{umlaut over (x)}+c{dot over (x)}+kx

A vibration isolator utilizes inertial forces m{umlaut over (x)} tocancel elastic forces kx. On the other hand, a damping device isconcerned with utilizing dissipative effects c{dot over (x)} to removeenergy from a vibrating system.

One important engineering objective during the design of an aircraftvibration-isolation system is to minimize the length, weight, andoverall size (including cross-section) of the isolation device. This isa primary objective of all engineering efforts relating to aircraft.

Another important engineering objective during the design ofvibration-isolation systems is the conservation of the engineeringresources that have been expended in the design of other aspects of theaircraft or in the vibration-isolation system. In other words, it is animportant industry objective to make incremental improvements in theperformance of vibration isolation systems which do not require radicalre-engineering or complete redesign of all of the components which arepresent in the existing vibration-isolation systems.

A marked departure in the field of vibration isolation, particularly asapplied to fixed- and rotary-wing aircraft is disclosed in commonlyassigned U.S. Pat. No. 4,236,607, titled “Vibration Suppression System,”issued Dec. 2, 1980, to Halwes, et al. (Halwes '607). Halwes '607 isincorporated herein by reference. Halwes '607 discloses a vibrationisolator, in which a dense, low-viscosity fluid is used as the “tuning”mass to counterbalance oscillating forces transmitted through theisolator. This isolator employs the principle that the acceleration ofan oscillating mass is 180 degrees out of phase with its displacement.

In Halwes '607, it was recognized that the inertial characteristics of adense, low-viscosity fluid, combined with a hydraulic advantageresulting from a piston arrangement, could harness the out-of-phaseacceleration to generate counterbalancing forces to attenuate or cancelvibration. Halwes '607 provided a much more compact, reliable, andefficient isolator than was provided in the prior art. The originaldense, low-viscosity fluid contemplated by Halwes '607 was mercury.

Since Halwes' early invention, much of the effort in this area has beendirected toward replacing mercury as a fluid or to varying the dynamicresponse of a single isolator to attenuate differing vibration modes.Examples of the latter are found in commonly assigned U.S. Pat. No.5,439,082, titled “Hydraulic Inertial Vibration Isolator,” to McKeown,et al. (McKeown '082), and U.S. Pat. No. 6,695,106, titled “Method andApparatus for Improved Vibration Isolation,” to Smith, et al (Smith'106). McKeown '082 and Smith '106 are incorporated herein by reference.

The Halwes vibration isolator, and similar isolators, providesparticular utility in the application of vibration control forhelicopters. In most current helicopters, the drive shaft (mast) andtransmission are rigidly connected together in a unit referred to as a“pylon.” The pylon is mounted to the airframe, and the engines aremounted to the airframe separate from the pylon assembly.

For example, FIG. 1 shows a prior-art configuration in which a pylon 11comprises a transmission 13 mounted to an airframe 15. Transmission 13is mounted using multiple links 17. An engine 19 is mounted to airframe15 near pylon 11 using multiple links 21. A coupling 23 couples anoutput of engine 19 to a shaft 25, which is coupled with coupling 27 toan input of transmission 13. Torque produced by engine 19 is transmittedthrough shaft 25 into transmission 13 for driving in rotation mast 29.Mast 29 is coupled to at least one rotor (not shown) for causingrotation of the rotor. Links 17 are shown as having integral isolators31, such as Halwes isolators, for isolating vibration transmittedthrough links 17 from pylon 11. Each end of each link 17 has aspherical-bearing rod end 33 a, 33 b for connecting links 17 to themounting locations on transmission 13 and airframe 15, respectively.

The Halwes vibration isolator has been incorporated in a pylon mountingsystem providing six degrees of freedom for the pylon relative to theairframe. The Six-Degree-of-Freedom (6DOF) pylon was developed anddisclosed by Halwes in the early 1980s and consisted of sixvibration-isolator links that successfully provided very low vibrationon a demonstrator aircraft. The links are arranged in a staticallydeterminant manner, so that steady loads, including torque, are carriedthrough the six links.

FIGS. 2 through 5 show prior-art pylon 6DOF assemblies having six links,at least some of the links having Halwes isolators. FIGS. 2 and 3 showoblique and top views, respectively, of pylon 35, which has aconfiguration of six links 17 that are attached in pairs to atransmission 37. An inner rod end 33 a of each link 17 is attached totransmission 13 at one of three mounting points 39 a, 39 b, 39 c, whichare located approximately equidistant from each other about theperiphery of transmission 13. Outer rod end 33 b of each link 17 isattached at one of three mounting points 41 a, 41 b, 41 c locatedapproximately equidistant from each other on an airframe.

FIGS. 4 and 5 show oblique and top views, respectively, of pylon 43,which has a configuration of six links 17 that are attached in pairs toa transmission 45. Inner rod ends 33 a of each of two pair of links 17are attached to one of mounting points 47 a, 47 b on opposite sides oftransmission 45, and a third pair of links 49 is attached totransmission 45 at a mounting point 51 located approximately equidistantfrom mounting points 47 a, 47 b. Each outer rod end 33 b is attached toan airframe at a mounting point 53 a, 53 b, 53 c, 53 d. Each link 49 hasan inner rod end 55 a attached to mounting point 51 and an outer rod end55 b attached to one of mounting points 53 c, 53 d. Links 49 have ashorter length than links 17, but links 49 also have integral Halwesisolators 56 and operate in the same manner as links 17.

Because each link 17, 49 has a rod end 33 a, 33 b or 55 a, 55 b on eachend, such that each link 17, 49 can only transmit loads along its axis,attenuating the axial vibration traveling through each link 17, 49results in dramatic reduction of vibration transmitted through the linksinto the airframe. However, the 6DOF pylon mounting is a “soft” mountingthat allows movement of the pylon, requiring 1) high performance driveshaft couplings to handle misalignments of the engine and transmission,2) decoupled controls to prevent unintended flight control inputs, and3) clearance to allow for motion of the pylon.

SUMMARY OF THE INVENTION

There is a need for a vibration-attenuating, hard-mounted pylon for anaircraft and for an active, vibration-attenuating mounting linkconfigured for use therewith.

Therefore, it is an object of the present invention to provide avibration attenuating, hard-mounted pylon for an aircraft and for anactive, vibration-attenuating mounting link configured for usetherewith.

A preferred embodiment of a pylon has six pylon mounting links formounting the pylon to an airframe. Each link is considered “near-rigid”and has a spherical-bearing rod-end on both ends such that the link canonly transmit axial loads. At least one of the links has a mass carriedwithin the link and selectively moveable by an actuating means along theaxis of the link in an oscillatory manner for attenuating vibrationstraveling axially through the link. The actuating means may be anelectromechanical, hydraulic, pneumatic, or piezoelectric system. Bymounting each link in a selected orientation relative to the otherlinks, the actuating means may be operated in a manner that attenuatesaxial vibration that would otherwise be transmitted through the link andinto the airframe.

The present invention provides for several advantages, including: (1)active vibration attenuation for various frequency ranges; (2) theability to use low-complexity connections, such as basic driveshaftcouplings, to attach the pylon to other components; and (3) the abilityto use transmission-mounted equipment, such as air-conditionercompressors.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, includingits features and advantages, reference is now made to the detaileddescription of the invention taken in conjunction with the accompanyingdrawings in which like numerals identify like parts, and in which:

FIG. 1 is a schematic side view of a prior-art pylon and engine mountedon a frame of an aircraft;

FIG. 2 is an oblique view of a prior-art pylon and mountingconfiguration;

FIG. 3 is a top view of the prior-art pylon and mounting configurationof FIG. 2;

FIG. 4 is an oblique view of a prior-art pylon and mountingconfiguration;

FIG. 5 is a top view of the prior-art pylon and mounting configurationof FIG. 4;

FIG. 6 is a side view of the preferred embodiment of a mounting linkaccording to the invention and used in pylons according to theinvention, a portion of the link being cutaway;

FIG. 7 is a side view of an alternative embodiment of a mounting linkaccording to the invention and used in pylons according to theinvention, a portion of the link being cutaway;

FIG. 8 is an oblique view of a preferred embodiment of a pylon andmounting configuration according to the present invention, the pylonmount comprising links according to the invention;

FIG. 9 is a top view of the pylon and mounting configuration of FIG. 8;

FIG. 10 is an oblique view of an alternative embodiment of a pylon andmounting configuration according to the present invention, the pylonmount comprising links according to the invention;

FIG. 11 is a top view of the pylon and mounting configuration of FIG.10;

FIG. 12 is a side view of a rotary-wing aircraft having a hard-mountedpylon according to the invention and a vibration-attenuation systemaccording to the invention; and

FIG. 13 is a schematic view of a vibration-attenuation system accordingto the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is directed to a pylon mounting configurationusing vibration-attenuating links, the invention being particularlyuseful with rotary-wing aircraft. The preferred embodiment is aconfiguration in which a pylon is hard-mounted to the aircraft usingmultiple links to limit movement of the pylon and to provide for active,tunable vibration treatment as the speed of rotation of the rotorchanges. The invention could be used on all rotorcraft to reducevibration transmitted from the pylon to the fuselage or from thefuselage to sensitive avionics, sight systems, or occupant seatingsystems. The invention also includes a vibration-attenuation system forcontrolling the operation of the links of the pylon.

The pylon configuration of the invention substitutes six links havingembedded oscillatory vibration attenuators for the links having Halwesfluid isolators in the Six Degree of Freedom (6DOF) pylon mountingarrangement. The attenuators of the invention are designed to be smallerand carried within each link. Oriented thus, they can attenuate theaxial vibration that would otherwise be transmitted through the link andinto the attached structure. Further, the links are considered“near-rigid,” so the pylon motion is reduced dramatically from thatallowed by a configuration using the Halwes isolators. Reducing movementof the pylon allows for the use of simple drive shaft couplings (e.g.,Thomas couplings) and transmission-mounted equipment such asair-conditioner compressors.

FIGS. 6 and 7 show example embodiments of the links according to theinvention. FIG. 6 is a side view of a link 57, with a portion of link 57shown in cutaway. Link 57 comprises an elongated cylindrical body 59having spherical-bearing rod ends 61 a, 61 b at opposite ends of body59, such that link 57 can only carry loads directed along itslongitudinal axis. Body 59 encloses an open volume 63, and a mass 65 ismoveably carried within volume 63. Mass 65 is moveably carried on, andcoaxial with, a voice-coil actuator 67, which comprises wire 69 coiledabout a rod 71. Rod 71 is fixedly attached within body 59. Wire 69 isconductively connected to wire leads 73 for connection to an electricalpower source. Mass 65 is formed of a magnetic material and/or carriespermanent magnets thereon.

In operation, when an electrical current is supplied to leads 73, thecurrent passes through wire 69 and creates a magnetic field, whichcauses movement of mass 65 within volume 63 and along the longitudinalaxis of link 57. Oscillating the direction of current flow in wire 69causes mass 65 to move in an oscillatory manner. The oscillatory forcecreated through oscillation of mass 65 may be used to counterbalancevibration traveling through link 57.

FIG. 7 is a side view of an alternative embodiment of a link accordingto the invention and including inertial devices for attenuatingvibration traveling through the links. Link 75, shown with a portion oflink 75 in cutaway, comprises an elongated cylindrical body 77 havingspherical-bearing rod ends 79 a, 79 b at opposite ends of body 77, suchthat link 75 can only carry loads directed along its longitudinal axis.Body 77 encloses an open volume 81, which is divided into two fluidchambers 83 a, 83 b, and a mass 85 is moveably carried within volume 63.Mass 83 acts as a piston within volume 81 and is sealed to an innersurface 87 of volume 81 with seals 89 near the ends of mass 85.Hydraulic fluid lines 91, 93 are in fluid communication with fluidchambers 83 a, 83 b, respectively, for providing fluid pressure to fluidchambers 83 a, 83 b. A fluid line 95 communicates fluid chambers 83 a,83 b for allowing fluid to pass from one chamber 83 a, 83 b to anotherof chambers 83 a, 83 b. A valve 97 may be used to control the flow offluid through fluid line 95.

When fluid pressure is supplied through one of lines 91, 93, the fluidpressure in the associated fluid chamber 83 a, 83 b acts on the adjacentsurface area of mass 85 and urges mass 85 toward the other of chambers83 a, 83 b along the longitudinal axis of link 75. Applying pressure tochambers 83 a, 83 b in an oscillating manner causes mass 85 to move inan oscillatory manner. The oscillatory force created through oscillationof mass 85 may be used to counterbalance vibration traveling throughlink 75.

While links according to the invention are shown as havingelectromechanical (link 57) and hydraulic (link 75) actuating means inthe inertial device, it should be understood that other means may beused, including, for example, pneumatic and piezoelectric means.

FIGS. 8 and 9 show oblique and top views, respectively, of a preferredembodiment of a “hard-mounted” pylon according to the present inventionand using links according to the invention. Pylon 99 comprisestransmission 101 and mast 103. In the configuration shown, pylon 99 isconfigured for mounting to an aircraft using link 57 in a type of 6DOFmounting configuration. An inner rod end 61 a of each link 57 isattached to transmission 101 at one of three mounting points 105 a, 105b, 105 c, which are located approximately equidistant from each otherabout the periphery of transmission 101. Outer rod end 61 b of each link57 is attached at one of three mounting points 41 a, 41 b, 41 c locatedapproximately equidistant from each other on an airframe.

FIGS. 10 and 11 show oblique and top views, respectively, of analternative embodiment of a “hard-mounted” pylon according to thepresent invention and using links according to the invention. Pylon 109comprises transmission 111 and mast 113. Inner rod ends 61 a of each oftwo pair of links 57 are attached to one of mounting points 115 a, 115 bon opposite sides of transmission 111. A third pair of links 57, whichare shorter in length than those in the other pairs, is attached totransmission 111 at a mounting point 115 c located approximatelyequidistant from mounting points 115 a, 115 b. Each outer rod end 61 bis attached to an airframe at a mounting point 117 a, 117 b, 117 c, 117d. Outer rod end 61 b of each link 57 attached to mounting point 115 cis attached to a mounting location 117 c, 117 d together with one oflinks 57 in the other pairs of links 57.

FIG. 12 is a side view of a helicopter having a pylon mountingconfiguration and vibration control system according to the invention.Helicopter 119 has a fuselage 121 and an empennage 123 extendingrearward from fuselage 121. A main rotor 125 is rotated by mast 127above fuselage 121, and a tail rotor 129 is carried on a rear portion ofempennage 123. An engine 131 is mounted within an upper portion offuselage 121 and produces torque that is transmitted through atransmission 133 to mast 127 for rotating rotor 125. Transmission 133and mast 127 form a pylon, which is mounted in helicopter 119 usingvibration attenuating links, such as links 57, in one of the pylonmounting configurations shown and described above. A computer-basedcontroller 135 for a vibration control system is carried on helicopter119 for controlling the operation of the actuating means of links 57.

FIG. 13 is a schematic view of a vibration control system 137 accordingto the present invention. Transmission 133 is mounted to fuselage 121with six vibration-attenuating links 57. A vibration sensor 139, 141 islocated near the outer end of each link 57 for sensing vibrations thatare transmitted through links 57 to fuselage 121. In addition, vibrationsensors 143, 145 may be located in other areas of helicopter 119 forsensing vibrations in selected areas, such as an occupant area, or insensitive equipment. Sensors 143, 145 may also be used to sensevibration entering fuselage 121 from empennage 123. Data cables 147,149, 151, 153 communicate data between controller 135 and vibrationsensors 139, 141, 143, 145, respectively. Cables 155, 157 communicateoperating commands and/or data between controller 135 and links 57. Forease of illustration, only two links 57 are shown as being incommunication with controller 135. However, in the preferred embodimentall links 57 are operated using at least one controller 135. It shouldalso be noted that system 137 may use more or fewer vibration sensors.

In operation, vibration sensors 139, 141, 143, 145 sense vibration inthe structures to which they are attached and communicate the vibrationdata to controller 135. Controller 135 uses the vibration data and avibration-attenuation algorithm to calculate the frequency and amount offorce required to attenuate the sensed vibrations to a selected degreeof attenuation. This attenuation may be a percentage reduction in thesensed vibrations or may be a reduction of the sensed vibrations to aselected level. To attenuate the vibrations, controller 135 commands theactuating means of each link 57 to move the internal mass at a selectedfrequency, acceleration, and/or distance traveled by the mass withineach link 57. Controller 135 may control the operation of links 57individually or in combinations of two or more links 57.

The present invention provides for several advantages, including: (1)active vibration attenuation for various frequency ranges; (2) theability to use low-complexity connections, such as basic driveshaftcouplings, to attach the pylon to other components; and (3) the abilityto use transmission-mounted equipment, such as air-conditionercompressors.

While this invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications and combinations of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thedescription.

1. A vibration-attenuating link for mounting a pylon on an aircraft, thelink comprising: a singular rigid body having opposing ends pivotallyconnected to both the pylon and a rigid structure of the aircraft, therigid body enclosing an interior volume; a first volume and a secondvolume, the first volume and the second volume being at least partlydefined by an interior surface within the interior volume of the rigidbody; a mass separating the first volume and the second volume, the massbeing configured as a piston such that the mass is moveably sealed tothe inner surface of the rigid body; a first fluid line in fluidcommunication with the first volume; a second fluid line in fluidcommunication with the second volume; a third fluid line in fluidcommunication only with the first and the second volume; and a fluiddisposed in the first volume, the second volume, the first fluid line,and the second fluid line; wherein the mass is moveably carried andtranslates within the interior volume of the rigid body in communicationwith the inner surface in response to commands by a controller, thecontroller being configured to move the mass in an oscillatory manner soas to create oscillatory forces; wherein the oscillatory forces reactagainst vibratory forces transferred into the body.
 2. The linkaccording to claim 1, wherein the body is cylindrical.
 3. The linkaccording to claim 1, wherein the oscillatory forces react against thevibratory forces approximate the first fluid chamber and the secondfluid chamber.
 4. The link according to claim 1, further comprising: avalve in at least one of the first fluid line and the second fluid line.5. The link according to claim 1, wherein the controller alternatelyapplies fluid pressure to the first volume through the first fluid lineand the second volume through the second fluid line so as to move themass in an oscillatory manner so as to create oscillatory forces; andwherein the flow of fluid through the third fluid line is controlled bya valve.